The present invention relates to switchable exhaust gas heat exchangers. Switchable exhaust gas heat exchangers which form the basis of the precharacterizing clause, are known, for example, from EP 1 030 050 A1. They are used in particular in exhaust gas recirculation lines of internal combustion engines, and specifically in exhaust gas recirculation lines of internal combustion engines of motor vehicles.
It is known in internal combustion engines to recirculate discharged exhaust gas to the fresh air intake side. The recirculation of exhaust gas in internal combustion engines serves to condition the exhaust gas. To optimize pollutant emissions and fuel consumption in the internal combustion engine, it may be expedient if exhaust gas discharged from the internal combustion engine is recirculated again to its air intake side. In this context, there are operating states, such as the cold start, in which it is particularly expedient for the exhaust gas temperature of the exhaust gas to be as high as possible, since this results, for example, in rapid internal heating of the internal combustion engine. In other operating states, it is preferable for the temperature of the recirculated exhaust gas to be reduced as much as possible, for example in order to achieve a greater density of the volumetric flow of the recirculated exhaust gas.
In this context it is known, for example from the document which forms the basis of the precharacterizing clause, to provide a switchable exhaust gas heat exchanger in the exhaust gas recirculation line, in which exhaust gas passed through the heat exchanger can be cooled or left uncooled as desired.
With a switchable exhaust gas heat exchanger forming the basis of the precharacterizing clause of this type, exhaust gas flows from an exhaust gas feed line through the switchable exhaust gas heat exchanger to an exhaust gas discharge. This creates the possibility of routing the exhaust gas which flows in at the exhaust gas feed line either through a first exhaust gas passage, in which there is arranged a heat exchanger through which coolant flows, or through a second exhaust gas passage, which bypasses the heat exchanger, to an exhaust gas discharge. There is a switching valve which switches the exhaust gas stream between the exhaust gas passages.